Fix middle of bridge not being redrawn when adding removing signals.

src/rail_cmd.cpp

@@ -1090,8 +1090,7 @@ CommandCost CmdBuildSingleSignal(TileIndex tile, DoCommandFlag flags, uint32 p1,
 					}
 				}
 			}
-			MarkTileDirtyByTile(tile);
-			MarkTileDirtyByTile(tile_exit);
+			MarkBridgeOrTunnelDirty(tile);
 			AddSideToSignalBuffer(tile, INVALID_DIAGDIR, GetTileOwner(tile));
 			YapfNotifyTrackLayoutChange(tile, track);
 		}
@@ -1538,8 +1537,7 @@ CommandCost CmdRemoveSingleSignal(TileIndex tile, DoCommandFlag flags, uint32 p1
 			ClrBitTunnelBridgeSignal(end);
 			_m[tile].m2 = 0;
 			_m[end].m2 = 0;
-			MarkTileDirtyByTile(tile);
-			MarkTileDirtyByTile(end);
+			MarkBridgeOrTunnelDirty(tile);
 			AddSideToSignalBuffer(tile, INVALID_DIAGDIR, GetTileOwner(tile));
 			YapfNotifyTrackLayoutChange(tile, track);
 			return CommandCost(EXPENSES_CONSTRUCTION, cost);

src/tunnelbridge.h

@@ -16,6 +16,7 @@
 
 void MarkBridgeDirty(TileIndex begin, TileIndex end, DiagDirection direction, uint bridge_height);
 void MarkBridgeDirty(TileIndex tile);
+void MarkBridgeOrTunnelDirty(TileIndex tile);
 
 /**
  * Calculates the length of a tunnel or a bridge (without end tiles)

src/tunnelbridge_cmd.cpp

@@ -80,6 +80,20 @@ void MarkBridgeDirty(TileIndex tile)
 	MarkBridgeDirty(tile, GetOtherTunnelBridgeEnd(tile), GetTunnelBridgeDirection(tile), GetBridgeHeight(tile));
 }
 
+/**
+ * Mark bridge or tunnel tiles dirty.
+ * @param tile Bridge head or tunnel entrance.
+ */
+void MarkBridgeOrTunnelDirty(TileIndex tile)
+{
+	if (IsBridge(tile)) {
+		MarkBridgeDirty(tile);
+	} else {
+		MarkTileDirtyByTile(tile);
+		MarkTileDirtyByTile(GetOtherTunnelBridgeEnd(tile));
+	}
+}
+
 /** Reset the data been eventually changed by the grf loaded. */
 void ResetBridges()
 {